Uncertainty Evaluation of Friction Velocity Measurements by Oil-Film Interferometry

Wind loads on structures and the wind environment around buildings are based on tests in boundary layer wind tunnels with corresponding scale parameters. The lower part of the troposphere boundary layer was simulated inside a small wind tunnel located at the Wind Engineering Centre of the Université de Moncton. The correct scale ratios of the boundary layer thickness combined with the roughness height are two of the most important scales to match. For small wind tunnels, roughness parameters related to the model boundary layer can be difficult to measure since scale ratios for wind load studies are expected to be in the range of 400–1000. Oil-film interferometry was used to determine the roughness parameters (shear stress, friction velocity, and roughness height) of the forced turbulent boundary layer inside the wind tunnel. In this work, the International Organization for Standardization (ISO) Guide to Expression of Uncertainty in Measurements was used to evaluate the standard uncertainty of the roughness parameters on the bottom wall of the wind tunnel. The standard uncertainty of the roughness parameters depends strongly on the oil viscosity and on the accurate measurement of the fringe spacing. Results show that the standard uncertainty of the shear stress and friction velocity determined by the interferometry technique can be less than 5% when the oil viscosity and the fringe spacing can be accurately measured with a standard uncertainty lower than 4% and 1%, respectively.

Calibration of Eddy Current Sensor Using Speckle Photography

Double exposure speckle is proposed to calibrate eddy current sensor in micro-displacement measurement for its simplicity, robustness and high resolution. The specklegram is taken as the vector of the displacement. The actual displacement of an object is calculated according to the speckle displacement on the spatial term, which is worked out according to the fringe spacing on the spectrum surface. A calibration system is proposed with proper speckle size and imaging magnification. Experiments showed that the accuracy of displacement measurement is 0.196um with an optical magnification 65.8. The calibration curve of the eddy current sensor is consistent with the result by a nanopositioning system.

Early results of AGN studies with the space VLB interferometer RadioAstron

The space element of the ground-space very long baseline (VLB) interferometer RadioAstron is a 10-meter radio telescope Spektr-R which was successfully launched in 2011. It covers four frequency bands from 0.3 to 25 GHz and provides baselines up to 350,000 km. This allows to study space objects with a resolution as high as about 10 microarcseconds. Fringes are found at all four bands of 92, 18, 6, and 1.3 cm. Science observations are ongoing. Early results of the RadioAstron AGN survey at extreme angular resolutions will be presented in the talk. In particular, AGN core emission is successfully detected at interferometer baselines up to 7.6 GLambda (or fringe spacing 27 microarcseconds) which is the current VLBI record. High radio brightness of AGN cores is found significantly above the known inverse-Compton limit. Implications to AGN jet emission models will be discussed. First results of RadioAstron space VLBI imaging of AGN jets will be also presented.

The Study of Polymer Material Transference Phenomenon Measurement Method

In this paper, for the transference phenomenon of high polymers, a method of measurement system based on sodium light and feisuo interference with digital image processing technology was proposed. At first, the system measurement scheme and method were explained and there were some experiments with micro moleculesIn the experiment, the high polymer is the mixture of acetone and organic glass by a certain ratio, the micro molecules are Acetone and ethanol; at last, the interference strips were collected at interval time by using the image control collection procedure and processed. After thinning the fringes, we calculated the fringe spacing distance by K-L transform, by measuring the fringe spacing change in the polymer transference of acetone and ethanol we draw the change rule of the Polymer material refractive index :in 10 mins, the fringe spacing became to 40 percent , the refractive index became 2.5 times and keep invariant for Polymer material; in 50 mins, the fringe spacing became to 56 percent ,the refractive index became 1.7 times and kept invariant for ethanol. That’s all, at the time of balance, it will not infect the capability of the Polymer material any longer.